WASHINGTON (Reuters) - Internet service providers clashed with Democrats and celebrities like "Star Wars" actor Mark Hamill ahead of a vote on the Trump administration's plan to revoke net neutrality rules barring the blocking or slowing of internet traffic.

The Federal Communications Commission is due to vote on Thursday on chairman Ajit Pai's plan to rescind so-called net neutrality rules championed by Democratic former President Barack Obama that treated internet service providers like public utilities.

Protesters including some members of Congress are expected to rally outside the FCC before the vote. The American Civil Liberties Union and consumer advocacy groups are also opposed to reversing net neutrality rules.

Apple Inc's <AAPL.O> co-founder Steve Wozniak and internet pioneers Tim Berners-Lee and Vinton Cerf joined several other technology titans in a letter on Monday asking the FCC to cancel the vote.

The 2015 rules barred broadband providers from blocking or slowing down access to content or charging consumers more for certain content. They were intended to ensure a free and open internet, give consumers equal access to web content and prevent broadband service providers from favoring their own content. Pai proposes allowing those practices as long as they are disclosed.

Pai's proposal marks a victory for big internet service providers such as AT&T Inc <T.N>, Comcast Corp <CMCSA.O> and Verizon Communications Inc <VZ.N> that opposed the rules and gives them sweeping powers to decide what web content consumers can get. It is a setback for Google parent Alphabet Inc <GOOGL.O> and Facebook Inc <FB.O>, which had urged Pai not to rescind the rules.

Michael Powell, a former FCC chairman who heads a trade group representing major cable companies and content creators, told reporters that internet providers would not block content because it would not make economic sense and consumers would not stand for it.

"They make a lot of money on an open internet," Powell said, adding it is "much more profitable" than a closed system. "This is not a pledge of good-heartedness, it's a pledge in the shareholders' interest."

A University of Maryland poll released this week found that more than 80 percent of respondents opposed the proposal. The survey of 1,077 registered voters was conducted online by the university's Program for Public Consultation from December 6-8.

Democrats have said the absence of rules would be unacceptable overturn the proposal if it is approved. Advocates of the net neutrality rules also plan a legal challenge.

Pai's proposal is "like letting the bullies develop their own playground rules," said Senator Ed Markey, a Massachusetts Democrat.

Many Republicans back Pai's proposal but want Congress to write net neutrality rules. Senate Majority Leader Mitch McConnell said the FCC would "return the internet to a consumer-driven marketplace free of innovation-stifling regulations."

Comcast said on Wednesday that "despite repeated distortions and biased information, as well as misguided, inaccurate attacks from detractors, our Internet service is not going to change."

New York Attorney General Eric Schneiderman said on Wednesday that his office had found more than 2 million fake comments were submitted to the FCC on the proposal. The FCC is expected to address the fake comments in the revised order that will be adopted on Thursday. Nearly 20 state attorneys general have asked the FCC to delay the vote until the issue of fake comments was addressed.

Washington Governor Jay Inslee said on Wednesday that the state plans to take steps to protect net neutrality rules. Pai has proposed blocking states from setting their own net neutrality rules.